Polishing felt



Feb. 25, 1941. F. H. HATELY 2,232,945

POLISHING FELT Filed June 15, 1959 INVENTOR F R/V555 H41! HATE 7 ATTORNEYS Patented Feb. 25, 1941 POLISHING FELT Furness Hall Hately, Greenwich, Conn, assignor to American Felt Company, New York, N. Y., a corporation of Massachusetts Application June 15, 1939, Serial No. 279,270

2 Claims.

The present invention relates to felts for use on glass polishing machines and the like, where the felts are subject to severe rubbing wear, moisture and high temperature during use and, therefore, require a firm body, tough texture and shrink resistance in that part constituting the wearing portion. I

The invention has been developed in the production of polishing felts for use on the polishing heads of glass polishing machines and, for convenience, a felt as developed for the particular use will be more particularly described to illustrate the principles of the invention.

In glass polishing machines as used in the manufacture of plate glass, the rotatable polishing heads usually present circular operating faces faced with felt to which is fed water dispersed rouge. The felt is secured in operative position on the polishing head by folding its corners up around the edge of the head and clamping the same securely by an encircling band or clamp. The head with the felt secured thereto constitutes a polishing unit of the apparatus. Usually several such units operate together.

The felts most commonly used are of a relatively dense, firm, thoroughly fulled quality usually composed of cattle hair or a mixture of cattle hair and goat hair. These felts are of considerable thickness, usually an inch or more, to provide durability in use; After 200 or 300 hours ofuse felts of present manufacture are worn to a thickness of perhaps to /2 ofan inch and then fail. I have determined that the failure of the felts is due at least in part to. the shrinkage of the center portion which occurs under the conditions of use. When polishing glass the felts are wet with water in which polishing compound is carried and in use they become heated due to the friction of the felt on the glass. Later when allowed to stand and cool or dry or both they shrink. The failure begins with a noticeable thinning down or necking of the felt on the diagonal lines at a distance approximately 3 to 8" from the periphery of a polishing head 27" in diameter. As the center portion shrinks while the corners are retained in place by being bent up and held by a band or clamp as described, a tensile stress is placed upon all of the fibres in. the diagonal lines and failure occurs first with the above mentioned necking and finally with a complete rupture between adjacent fibres resulting in an actual opening occurring in the felt. Two of such openings may be tolerated before the sheet must be removed from operation. The limiting life, therefore, is the period of time that the felts will sustain the polishing a'ctionbefore more than two such tears occur. Analysis forming the basis ofthe present invention had for its object the determination of means to prevent shrinkage of such central portion with resultant diagonal stresses and ultimate tearing.

I have found that the deficiencies of the polishing felts heretofore produced result from certain features. of the usual method of manufacture. These felts are ordinarily made in squares of the size required for use. The original sheets are hardened to prepare them for fulling and then rolled up and fulled in the fulling machine.

After fulling the squares are pressed at high temperature, about 200 F. while still moist to compress and flatten the felt.

There is a considerable tendency for the corners of the square to felt more thoroughly in the fulling machine than does the center portion. Asa result the corners are more dense and correspondingly less flexible whereas the centers are less thoroughly felted, less dense and subject to shrinkage in use. This shrinkage, under the conditions of use as above explained, appears to be a principal cause of the failure of the felts in use.

If the fulling operation of the process as heretofore practiced is continued until the central area of the square is dense and no longer subject to shrinkage, then the corner portions are too dense, hard and inflexible satisfactorily to be secured to the polishing'head. Also, if the felt is too dense the polishing compound does not readily penetrate into the felt as is desirable but tends to cake on the surface of the felt.

In order to provide a more durable polishing felt it is desirable to make provision for increasing the density andfirmness of the center por tion without excessive fulling and relatively to increase the flexibility of the corner' portions. In the embodiment of the invention more particularly herein described this is accomplished by making the center portion of the soft lay-up or sheet relatively heavier and the marginal corners relatively of less weight, in other words by making the center portion heavier than the corner portions.

When the sheets of this type are full-ed, the

and inflexible that they will fail when folded about the head and secured thereto.

When the increase of the thickness of the center portion of the sheet and the extent of fulling are suitably correlated to each other, it is possible to produce a felt square of substantially uniform density and flexibility throughout its whole area.

The nature and objects of the invention will be better understood from a description of a particular embodiment illustrating the principles of the invention for the purposes of which description reference should be had to the accompanying drawing forming a part hereof and in which- Figure 1 is a sectional view of a built-up sheet ready for compression and felting,

Fig. 2 is a plan view showing a part in section,

Fig. 3 is a perspective view of a polishing head with the felt square applied thereto, a part being shown in section.

The felt square shown is produced by laying up a series of batts each comprising carded Webs to form the soft sheet, then hardening. and fulling the same in accordance with usual practice. As heretofore produced the original lay-up or sheet has been of uniform thickness. In the illustrative embodiment of the present invention, the center portion of the sheet is made of the same or greater thickness than heretofore, but the marginal portions are of less thickness.

As shown, the sheet 5 is composed of a number of batts 6 at least one of which, as indicated at I, is circular and of a diameter substantially equal to the width of the other batts which are square. The sheet is reduced in size by fulling until the width of the sheet is substantially equal to the diameter of the polishing head with which the felt is designed to be used. By this the polishing portion of the finished felt is thicker and denser and the marginal securing portions are of less weight and more flexible. The edges of this rounded center section I are preferably more or less scarfed when layed up, as indicated at 8, to avoid the eifect of an abrupt shoulder at the edge of the thicker central section with resultant poor hardening.

The soft lay-up is of considerable thickness, for example one to three feet and during the hardening and fulling operations it is compacted and condensed to form a very heavy, dense, hard, compact, durable, wear-resisting felt of a thickness of about one inch suitable for use to withstand the severe service for which it is designed. The amount of material layed as a central circular portion may amount to, for example, about 15% of the sheet. This percentage of the circular section is not particularly critical, yet if it is too small the desired extra central fulling is not obtained and, therefore, the objectionable shrinking in use is not avoided.

The sheet shown is hardened to a thickness of perhaps one inch after which it is rolled up and tied in rolled condition for fulling. A number of such rolls are then subjected to kneading or pounding in the fulling machine as is usual practice. The fact that the corner portions are of less thickness seems to affect the fulling operation. In any event, the resultant felts have dense central operative portions which are resistant to shrinking in use and flexible corner portions which can be readily folded over the edge of a polishing head and secured by usual fastening devices. In Fig. 3 such a felt square is shown as applied to the conventionally indicated head 9 with a band I0 securing the relatively flexible corner portions II.

The material used may consist of wool or hair such as cattle and goat hair or mixtures thereof. A felt made mainly or entirely of wool is superior in some respects but is more expensive. A mixture of cattle hair and goat hair can be made to produce a very durable felt and at relatively low cost.

I claim:

1. A felt square for use on a polishing machine having a hard, dense, non-shrinkable center portion of a size substantially equal to the size of a polishing head on which it is to be used and outer portions of less thickness and more flexibility for connection to fastening devices.

2. A felt for use on a polishing machine comprising a plurality of layers of material felted together at least one of which layers is of a size substantially equal to the size of a polishing head on which the felt is to be used and at least one of which layers is larger to provide fastening portions for securing to the polishing head.

FURNESS HALL HATELY. 

